In recent years, in order to improve fuel efficiency and reduce CO2, development of a high-efficiency engine to achieve small size, low NOX and high output is in progress.
Since the high-efficiency engine is under conditions of high-boost, high-compression, and lean fuel concentration of the fuel-air mixture, thus it is in an environment that igniting with a spark is difficult.
In order to start combustion in such an internal combustion engine which is difficult to ignite with high efficiency, an ignition system with a quick burning rate and an excellent ignitability is desired.
An internal combustion engine that injects fuel directly into a cylinder having a first electrode, a second electrode that surrounds the first electrode, an ignition chamber that communicates with a combustion chamber through an opening formed between the first and second electrodes, an active species generating unit that generates active species in the ignition chamber by applying a voltage between the first and second electrodes, and a control unit that varies an operating time of the active species generating unit is disclosed in Japanese Patent Application Laid-Open Publication No, 2010-37949.
In the internal combustion engine mentioned above, a fuel injector and the active species generating unit are disposed so that the active species are drawn into the cylinder from the ignition chamber.
However, the active species generating unit as in the Publication '949, the opening is disposed so as to be flush with an inner wall of a cylinder head of the engine in a state where a position of a tip of a center electrode matches an opening end of the ignition chamber, and has a structure to draw the active species generated in the ignition chamber (discharge space) into the combustion chamber using an air flow flowing in the combustion chamber.
Therefore, since a volume ignition which has occurred in the ignition chamber is drawn into the combustion chamber before it grows to a flame capable of igniting air-fuel mixture in the combustion chamber by flame propagation, it becomes difficult to ignite a lean air-fuel mixture.
Further, since it has a structure in which the ignition chamber is retracted inside the cylinder head, diffusion of the energy into the cylinder head is large, and energy applied is not used for ignition in an efficient manner. Thereby, it is found that the air-fuel ratio cannot be increased above a certain level in the internal combustion engine with limited power supply such as in a real vehicle.